I have tried Pecans on the advice of an old timer. I too may have over done it and ended up with a bitter bite. This was back when I thought that more smoke was the answer and knew nothing about the "Thin Blue Smoke".
I have read that traditionally and regionally almost anything goes as a source of fuel or smoke flavor. Ya know, some folks have cooked on dried, er, ah, um, well, turds! Corn cobs is another one that I have heard of, but I have tried neither, thank you.
Back to the nuts, Hickory and Pecan that is. It was the shells or hulls that were used, the meat/fruit would have been too valuable to burn as the story goes (although round these parts it would seem like there is an excess) I may try Pecan shells again some day and this time I will keep the smoke in check.